One major problem plaguing internal combustion engines is the so-called pumping loss which occurs during part throttle operation of the engine.
When an internal combustion engine operates at part throttle, a vacuum is developed downstream of the throttle valve. This negative pressure is transmitted to the combustion chamber of the engine during the induction phase of operation thereof. This tends to resist the movement of the piston, in the case of a reciprocating type internal combustion engine, in the direction of bottom dead center (BDC) due to the pressures differential developed across the piston. As a result some of the power developed during the power stroke of the piston is wasted in drawing the piston against the vacuum prevailing in the combustion chamber during the induction stroke thereof.
In order to partially overcome this pumping loss problem, a number of so-called "split mode" operation engines have been proposed wherein during part throttle operation, such as cruising and deceleration, some of the cylinders are disabled. However these arrangements, while partially solving the problem have encountered other drawbacks in the form of jolting induced by the sudden torque output changes occurring upon abling and disabling of one or more of the cylinders. Moreover the undue complexity of workable arrangements tends to be prohibitive.
Hence there still exists the need for an arrangement which can completely eliminate the pumping loss problem.